Buoyancy

Article By:

Streeter, Victor L. Department of Civil Engineering, University of Michigan, Ann Arbor, Michigan.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.099500

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• Buoyancy, published June 2014:Download PDF Get Adobe Acrobat Reader

The resultant vertical force exerted on a body by a static fluid in which the body is submerged or floating. Buoyancy is the upward force exerted by a fluid (liquid or gas) on a body that is placed within it (see illustration). The buoyant force F_B acts vertically upward, in opposition to the gravitational force. Its magnitude is equal to the weight of fluid displaced (a line of reasoning that is referred to as Archimedes' principle), and its line of action is through the centroid of the displaced volume, which is known as the center of buoyancy. Mathematically, the buoyant force equation is F_B = γV, where γ is the specific weight of fluid (weight per unit volume) and V is the displaced volume of fluid, respectively. By weighing an object when it is suspended in two different fluids of known specific weight, the volume and weight of the solid may be determined. In addition, the magnitude of the buoyant force must be given by the difference of vertical components of fluid force on the lower and upper sides of the body. See also: Archimedes' principle; Hydrostatics

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